docs: def _on_message(self, body, message):
          """What to do when a message is received.
  
          This is a kombu consumer callback taking the standard
          ``body`` and ``message`` arguments.
  
          Note that if the properties of the message contains
          a value for ``reply_to`` then a proper implementation
          is expected to send a reply.
  
          """
          if message.properties.get('reply_to'):
              handler = self.handle_call
          else:
              handler = self.handle_cast
  
          def handle():
              # Do not ack the message if an exceptional error occurs,
              # but do ack the message if SystemExit or KeyboardInterrupt
              # is raised, as this is probably intended.
              try:
                  handler(body, message)
              except Exception:
                  raise
              except BaseException:
                  message.ack()
                  raise
              else:
                  message.ack()
          handle()